A typical engine brake operates in a vehicle in such a manner that a shift ratio of a gear is adjusted downward. However, since a shift stage is adjusted downward, an excessive load is applied to each part of the engine, and thus the life of an engine may be shortened.
In one method for solving the above problem, an engine brake using compressing to forcibly open an exhaust valve at the close of a compression stroke of the engine to prevent a combustion stroke of the engine from being performed to maximize an effect of the engine brake is provided.
FIG. 1 is a graph illustrating a displacement of a valve lift at the time of using an engine brake using decompressing according to the related art.
The engine brake using decompressing according to the related art is configured to include a socket brake to be supplied with engine oil when the engine brake is operated. In this configuration, the engine brake using decompressing vertically moves a piston by the supplied engine oil to remove a gap between a valve and a rocker arm to forcibly open an exhaust valve at the close of a compression stroke.
The socket brake opens the exhaust valve at the close of the compression stroke to activate the brake on the vehicle, thereby maximizing the effect of the engine brake. However, when the engine oil is introduced into the socket brake once, since the engine oil is not discharged, the valve may be further opened by the oil pressure which is formed in the socket brake. Therefore, the valve contacts the piston at a portion illustrated by ‘A’ of FIG. 1 and performance may deteriorate.
To improve the problem, the engine brake using decompressing from a reset unit is provided at one side, but has a problem in that a reset starting pressure is high and a reset operation may be poor due to a non-uniform contact with a housing when the piston in the socket brake ascends and descends.
Recently, replacing a large engine by improving an output of a middle engine, (engine downsizing) has been applied, but the engine brake using decompressing may be not be sufficiently applied due to a size of the engine and may not often meet regulations about braking performance.